The story of Evander Holyfield's career can be told by its numbers.

Nicknamed "The Real Deal", Holyfield is the only four-time heavyweight world champion and has fought 22 title bouts in 20 years since moving up as undisputed cruiserweight champ.

He's beaten Mike Tyson twice, and counts George Foreman and Larry Homes among other wins.

But when Holyfield bids for a fifth world title by challenging unbeaten WBO champion Sultan Ibragimov on Saturday, it will be only six days before his 45th birthday, a number that has many wondering if he should even be allowed in the Khodynka Arena ring.

After losing a unanimous points decision to journeyman Larry Donald at Medison Square Garden in 2004 for his third straight defeat, Holyfied was banned from fighting again in New York on the grounds of "diminished skils".

But following a two-year break, he went to Texas and got four straight wins, albeit over modest opposition, to earn another title shot when WBA champion Ruslan Chagaev withdrew because of injury.

Holyfield could become the second-oldest man to win a heavyweight title, behind Foreman after he beat Michael Moorer for the WBA belt in 1994 at 45, and he is adamant that he deserves a chance to not only beat the 32-year-old Ibragimov but also unify the various titles.